Power generation system and method to operate

ABSTRACT

A power generation system includes an oxy-fuel-burner, a steam cycle, and a recirculation line for feeding a part of working media of the steam cycle into the oxy-fuel-burner. A system and a method provides at least one first feed-water-preheater and wherein the steam cycle joins into the recirculation line downstream the at least one first feed water pre-heater and extracting a tenth working-media-stream from the steam cycle, extracting an eighth working-media-stream as carbon-dioxide downstream the first condenser, wherein the at least one first feed water-preheater is heated with a working media stream extracted from the first steam turbine, namely a fifth working-media-stream.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2014/055725 filed Mar. 21, 2014, and claims the benefit thereof. The International application claims the benefit of European Application No. EP13160404 filed Mar. 21, 2013. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a power generation system comprising an oxy-fuel-burner and a steam cycle.

BACKGROUND OF INVENTION

Power generation systems and respective methods to operate such systems are known for a long time since mechanical power or electrical power is generated especially by burning a fuel with an oxygen containing gas. Recently concerns came up about carbon-dioxide content in air increasing up to an amount where a so called green-house effect might occur. Since such awareness is rising several projects are initiated to reduce the emission of carbon-dioxide. One of those projects is burning a fuel with an oxygen containing gas other than air to a avoid the generation of NOx (nitrogen oxides) and to avoid the mixing of essential inert components with the carbon-dioxide generated during combustion to more easily enable the separation of carbon-dioxide from the exhaust gas generated. This easy separation simplifies storage of pure carbon-dioxide in a final storage capacity. Essentially pure carbon-dioxide can further better be used for subsequent chemical processes. The oxygen containing gas is basically pure oxygen with minor impurities generated by for example an air separation unit, which can be of conventional membrane type. In the context of this invention an oxy-fuel-burner is characterized by burning basically a fuel with an oxygen containing gas wherein said oxygen containing gas has significant higher oxygen content than ambient air or wherein oxygen is its main component or wherein said oxygen containing gas is preferably pure oxygen with some impurities. This oxygen containing gas may contain some further additives but its main component is preferably oxygen.

One known power generation system is disclosed in U.S. Pat. No. 7,021,063 B2, which deals with an oxy-fuel-burner respectively gas generator comprising a recuperative heat exchanger for reheating of steam that has passed a first expansion machine stage, which heat exchanger is heated by outlet steam respectively exhaust from said gas generator.

The total efficiency of a conventional power generation system with an oxy-fuel-burner is significantly below the efficiency of an ordinary power generation system if the energy consumption of the air separation unit is considered. The efficiency is therefore to be improved to make this technology economically feasible and to have a positive effect on the environment.

SUMMARY OF INVENTION

It is an object of the invention to improve the efficiency of the known power generation system comprising an oxy-fuel-burner.

This object of enhancing the efficiency of the incipiently defined power generation system is achieved by a power generation system according to the claims. Further this object is achieved by a method according to the claims.

One aspect of the proposed improvement of the power generation system respectively the method according to the invention is the addition of heat exchangers for preheating of the re-circulated feed water submitted to the oxy-fuel-burner for mixing into exhaust stream of the oxy-fuel-burner (being a working media for a steam cycle). According to the invention by preheating with extraction steam the cycle performance is improved.

In the cycle according to the invention the steam respectively working media (substantially exhaust-fluid of the oxy-fuel-burner) taken from the steam turbine(s) contains carbon-dioxide in a substantial concentration, typically more than 5%, in particular about 10% by volume, which makes the cycle much different from a conventional steam cycle. The carbon-dioxide led to the pre-heaters is advantageously separated from the pre-heaters and then collected to be routed to an export carbon-dioxide stream. In particular a carbon-dioxide compression process for the delivery to a final user—for example enhanced oil recovery or methane synthesis—is integrated in the power generation system respectively method.

A further beneficial improvement of the process according to the invention is obtained by providing a recuperator respectively first heat exchanger downstream said oxy-fuel-burner before the exhaust-fluid of the oxy-fuel-burner (a first working-media-stream) enters a steam turbine. This heat exchanger respectively recuperator re-heats steam respectively the first working-media-stream that has passed a first expansion through said steam turbine, wherein the exhaust-fluid from said oxy-fuel-burner is heating a working-media-stream from said steam turbine. This heat exchanger provides a certain protection for the downstream steam turbine as it provides some heat capacity damping thermal gradients from upstream equipment control variations or disturbances. Further this heat exchanger assist in protecting the turbine from possible water droplets carried over from said oxy-fuel-burner.

Said oxy-fuel-burner according to the invention is basically a gas generator generating an exhaust gas respectively exhaust fluid from a fuel burned or combusted with essentially pure oxygen. This exhaust gas is referred to as exhaust-fluid since it might contain liquid components or parts of the fluid might condense to a liquid. As this exhaust-fluid is a burned fluid (thus exhaust in this respect) of the oxy-fuel-burner but also a medium for the steam cycle, it is also called working-media-stream in this document. All modifications and processing of this working-media stream within the steam cycle will also be called working-media stream.

Another beneficial improvement of the invention is given by providing at least one adjustable valve to control the flow through said recirculation line. This control feature allows maintaining the desired exhaust-fluid temperature downstream said oxy-fuel-burner (thus also called burner-discharge-fluid) respectively before said exhaust-fluid or working-media-stream enters any turbine equipment. Advantageously a control unit controls the position of said adjustable valve in the recirculation line according to a temperature measurement upstream a turbine (i.e. steam turbine) of the power generation system. This control unit is designed such that it receives the measurement results from temperature measurement and submits control signals to said control valve. The control method in particular is designed such that the valve opens further when exceeding a temperature limit is recognized. Further the valve control unit can be designed such that upper limits of temperature increases respectively steep temperature transients in a turbine of the power generation system are avoided.

Another embodiment provides a degasification port at said at least one feed water pre-heater to collect gaseous carbon-dioxide from the condensing exhaust-fluid.

Another embodiment of the invention provides an air separation unit upstream of said oxy-fuel-burner to advantageously separate oxygen from ambient air to be burned with a fuel in said oxy-fuel-burner. This air separation unit can be of a membrane type.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned attributes and other features and advantageous of this invention and the manner of attaining them will become more apparent and the invention itself will be understood by reference to the following description of the currently known best mode of carrying out the invention taken in conjunction with the accompanying drawings, wherein

FIG. 1 shows a schematic flow diagram of an oxy fuel power plant comprising the arrangement according to the invention and depicting the method according to the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a schematic depiction of a simplified flow diagram showing a power generation system and illustrating a method according to the invention. Fuel F and oxygen O₂ from an air separation unit ASU are both elevated to a higher pressure level by compressors C1, C2, C3, C4, C5 which compressors C1, C2, C3, C4, C5 are respectively provided with intercoolers INT1, INT2, INT3 before both fluids are injected in an oxy-fuel-burner OXB at a pressure of for example 150 bar. In said oxy-fuel-burner OXB—which can also be considered as a gas generator—combustion takes place of said fuel F with said oxygen O₂ generating exhaust gas hereinafter referred to as exhaust-fluid or first burner-discharge-fluid. This exhaust-fluid will be modified as explained in the paragraph below and converted to a first working-media-stream EXH1—and exits said oxy-fuel-burner OXB and enters a first heat exchanger HEX1 (wherein the first working-media-stream EXH1 heats a second medium).

The temperature of said first working-media-stream EXH1 is adjusted by controlling a flow of evaporating media—particularly water as medium—as recirculating stream to the oxy-fuel-burner OXB to be boiled off and thus cool the first burner-discharge-fluid to the right temperature (resulting in the first working-media-stream EXH1 then) to subsequently enter a second steam turbine ST2.

Downstream said first exchanger HEX1 said first working-media-stream EXH1 is expanded in said second steam turbine ST2, which is a high pressure steam turbine (high pressure means that this pressure level is higher than the pressure level of the downstream turbine—a first steam turbine ST1).

The first working-media-stream EXH1 exiting said second steam turbine ST2 is divided in a second exhaust-fluid-stream or second working-media-stream EXH2 and a third exhaust-fluid-stream or third working-media-stream EXH3, wherein in particular approximately above 90% of said first working-media-stream EXH1 becomes said third exhaust-fluid-stream EXH3.

Downstream said second steam turbine ST2 said third working-media-stream EXH3 enters said first heat exchanger HEX1 to be reheated taking thermal energy from said first exhaust-fluid-stream EXH1 coming from said oxy-fuel-burner OXB.

The presence of the second steam turbine ST2 and the first heat exchanger HEX1 may be optional.

Further downstream said third working-media-stream EXH3 enters a first steam turbine ST1 to be expanded from approximately 40 bar pressure down to a pressure of 0.2 bar. The pressure values are meant as examples. Said first turbine ST1 comprises several extractions of fluid streams so that said expanded third working-media-stream EXH3 is reduced to a seventh exhaust-fluid-stream or seventh working-media-stream EXH7 by extraction of a fourth exhaust-fluid-stream or fourth working-media-stream EXH4, extraction of a fifth exhaust-fluid-stream or fifth working-media-stream EXH5 and extraction of a sixth exhaust-fluid-stream or sixth working-media-stream EXH6. Downstream said first steam turbine ST1 said seventh working-media-stream EXH7 is partly liquefied in a first condenser CON1 (or more generally, in a water separator), which is equipped with a degasifier to separate said seventh working-media-stream EXH7 into a gaseous eighth exhaust-fluid-stream or eighth working-media-stream EXH8 and a liquid ninth exhaust-fluid-stream or ninth working-media-stream EXH9 both exiting said first condenser CON1. Said eighth working-media-stream EXH8 is basically gaseous carbon-dioxide and further downstream compressed in an intercooled multistage compressor MCP consisting of the stages CP1, CP2, CP3 and the intercooling heat exchangers INT3, INT4. Said multistage compressor MCP may receive further gaseous streams of carbon-dioxide at several intermediate pressure levels of compression to be compressed for subsequent usage, here indicated as storage STO.

Downstream said first condensers CON1 said ninth working-media-stream EXH9 it delivered to a higher pressure level by a first feed water pump FWP1, which has again an output of a feed-water-pump-output-stream. At a downstream division point DIV1 (which can be located at many different positions in the cycle, though) said ninth working-media-stream EXH9—more precisely: said feed-water-pump-output-stream—is split into a tenth exhaust-fluid-stream or tenth working-media-stream or extraction-fluid-stream EXH10—which basically consists of liquid water H₂O—and an eleventh exhaust-fluid-stream or eleventh working-media-stream EXH11, which enters a downstream mixing pre-heater and degasifier MPD. In said mixing pre-heater and degasifier MPD said eleventh working-media-stream EXH11 mixes with said sixth working-media-stream EXH6 extracted from said first steam turbine ST1 to increase the temperature and further mixes with a 22nd exhaust-fluid-stream or 22nd working-media-stream EXH22, which is throttled by a valve TH3 into said mixing pre-heater and degasifier MPD. The gaseous amount generated in said mixing pre-heater and degasifier MPD is directed to said multistage compressor MCP as a twelfth exhaust-fluid-stream or twelfth working-media-stream EXH12. The liquid amount from said mixing pre-heater and degasifier MPD is delivered to a downstream second feed-water-pump FWP2 as a thirteenth exhaust-fluid-stream or thirteenth working-media-stream EXH13. Further downstream said thirteenth working-media-stream EXH13 is heated-up in a second sub-cooler SCO2 exchanging heat with said 22th working-media-stream EXH22 before the latter enters said mixing pre-heater and degasifier MPD. Further downstream said thirteenth working-media-stream EXH13 enters in the following order a first feed water pre-heater WPH1, a first (optional) sub-cooler SCO1, a second (optional) feed water pre-heater WPH2, a third (optional) heat exchanger HEX3 and a third (optional) feed water pre-heater WPH3 and a second (optional) heat exchanger HEX2.

As already indicated the division point DIV1 can be positioned also at other positions in the cycle.

Downstream this pre-heating sequence said thirteenth working-media-stream EXH13 joins or leads into said recirculation line RCL through an adjustable valve WSV to be injected into said oxy-fuel-burner OXB to adjust the temperature of said first working-media-stream EXH1 as said above mentioned cooling media.

Said third feed water pre-heater WPH3 is heated by said second working-media-stream EXH2 extracted from said second steam turbine ST2 downstream passing said second heat exchanger HEX2 transferring thermal energy to said thirteenth working-media-stream EXH13. Said third feed water pre-heater WPH3 splits the hot side of this heat exchange into a gaseous component supplied to the multistage compressor MCP as an eighteenth exhaust-fluid-stream or eighteenth working-media-stream EXH18. The liquid component of the hot side of the third feed water pre-heater WPH3 is provided as a heating fluid through a first throttle TH1 into said second feed water pre-heater WPH2 as 20^(th) exhaust-fluid-stream or 20^(th) working-media-stream EXH20.

Said second feed water pre-heater WPH2 subsequently receives said fourth working-media-stream EXH4 from said first steam turbine ST1 to heat-up said thirteenth working-media-stream EXH13.

Said second feed water pre-heater WPH2 discharges a gaseous sixteenth exhaust-fluid-stream or sixteenth working-media-stream EXH16—consisting basically of carbon-dioxide—and a liquid 21st exhaust-fluid-stream or 21st working-media-stream EXH21 both resulting from said incoming fourth working-media-stream EXH4 and said 20^(th) working-media-stream EXH20. Said 21st working-media-stream EXH21 enters the heating side of said first sub-cooler SCO1 and further downstream enters said first feed water pre-heater WPH1 through a second throttle valve TH2 on the heating side.

Partly already explained, said first feed water pre-heater WPH1 receives said fifth working-media-stream EXH5 from said first steam turbine ST1 to heat-up said thirteenth working-media-stream EXH13.

Further, said first feed water pre-heater WPH1 discharges a gaseous fourteenth exhaust-fluid-stream or fourteenth working-media-stream EXH14—consisting basically of carbon-dioxide—and the liquid 22nd working-media-stream EXH22 both resulting from said incoming fifth working-media-stream EXH5 and said 21st working-media-stream EXH21. Said 22nd working-media-stream EXH22 enters the heating side of said second sub-cooler SCO2 and further downstream enters said mixing pre-heater and degasifier MPD through said third throttle valve TH3 on the heating side.

Said first steam turbine ST1 and said second steam turbine ST2 both drive at least one generator GEN to produce electrical power. As an alternative a direct drive can be provided for example for a compressor or any other unit to be driven.

Said first condenser CON1 can be cooled by ambient air, ambient water from a sea or a river or it can be a water spray condenser cooling the fluid to be condensed by water jet. Water can be provided by for example water extracted from said power generation system cooled and re-injected.

To prevent accumulation of undesired products in the cycle a water treatment WT can be inserted for example in said recirculation line RCL or at another location in the cycle. Alternatively or in addition (as shown in the FIGURE) another water treatment WT can be inserted upstream of the extraction of water H₂O as the tenth extraction-fluid-stream EXH10. This location would also improve the quality of water to be extracted for any potential subsequent usage.

It has to be noted that the extraction-fluid-stream EXH10 could be extracted at a lot of different positions in the cycle.

The steam cycle RC is operated with the working-media-streams EXH1, EXH7, EXH9, EXH11, EXH13. New fluid is provided via the first working-media-streams EXH1, some of the fluid is also extracted from the cycle, e.g. working-media-streams EXH8, EXH12, EXH14, EXH16, EXH18.

In an embodiment, the separation of carbon dioxide (CO2) from the first feed water pre-heater WPH1 (or the other feed water pre-heaters WPH2, WPH3) may differentiate from known feed water preheaters found in other steam cycles, since the magnitude of gas to be separated may be substantial, many percent of the steam turbine extraction flow (here: EXH2 or EXH4 or EXH5), whereas in known condensers just some ppb (part per billion) levels are separated during normal operation.

Some of the features as explained in the embodiment above are optional. The following setup is sufficient:

A power generation system PGS comprising—an oxy-fuel-burner OXB, wherein said oxy-fuel-burner OXB is made to generate a first burner-discharge-fluid from burning fuel F with an oxygen containing gas O2, said oxygen containing gas O2 having oxygen content which is higher than the oxygen content of ambient air, —a recirculation line RCL for feeding a first liquid, particularly water, into said oxy-fuel-burner OXB to mix with said generated first burner-discharge-fluid to a first working-media-stream EXH1, —a steam cycle RC operated with said first working-media-stream EXH1, —wherein said steam cycle RC comprises at least one first steam turbine ST1 expanding at least a part of said first working-media-stream EXH1, namely a third working-media-stream EXH3, wherein said first steam turbine ST1 has at least one output port for expanded fluid, one of which providing a seventh working-media-stream EXH7, —wherein said steam cycle RC comprises at least one first water separator CON1, particularly a condenser, downstream said first steam turbine ST1 condensing part of said seventh working-media-stream EXH7, wherein said first water separator CON1 has at least one output port for condensed fluid, one of which providing a ninth working-media-stream EXH9, —wherein said steam cycle RC comprises at least one first feed-water-pump FWP1 downstream of said first water separator CON1 delivering said ninth working-media-stream EXH9 to a higher pressure level, with an output of a feed-water-pump-output-stream, wherein, said steam cycle RC comprises at least one first feed-water pre-heater WPH1 downstream said first feed-water-pump FWP1 heating at least a part of said feed-water-pump-output-stream, namely a thirteenth working-media-stream EXH13, —wherein said steam cycle RC leads into said recirculation line RCL downstream said at least one first feed water pre-heater WPH1 feeding said thirteenth working-media-stream EXH13 into said recirculation line RCL as said first liquid, —wherein a part of working media in said steam cycle RC is extracted from said steam cycle RC, particularly downstream said first feed-water-pump FWP1, as a tenth extraction-fluid-stream EXH10, said tenth extraction-fluid-stream EXH10 being particularly water, —said first water separator CON1 further extracts carbon-dioxide from said seventh working-media-stream EXH7 via a further output port of said first water separator CON1 as an eighth carbon-dioxide-stream EXH8, —wherein one of said output ports of said first steam turbine ST1 provides a fifth working-media-stream EXH5 and wherein said at least one first feed water-pre-heater WPH1 is heated via said fifth working-media-stream EXH5.

The following method steps will be performed for such a system:

Method to operate a power generation system (PGS) defined by the following steps: —generating a first burner-discharge-fluid from burning an oxygen containing gas (O2) and fuel (F), —wherein an oxygen content of said oxygen containing gas (O2) is higher than the oxygen content of ambient air, —providing a steam cycle RC comprising at least one first steam turbine ST1, at least one first water separator CON1, particularly a condenser, downstream said first steam turbine ST1, at least one first feed-water-pump FWP1 downstream said first water separator CON1, at least one first feed-water-preheater WPH1 downstream said first feed-water-pump FWP1, —extracting a part of working media from said steam cycle RC by a recirculation line RCL and feeding a first liquid, particularly water, as said part of said working media into said oxy-fuel-burner OXB to mix with said generated first burner-discharge-fluid to result in a first working-media-stream EXH1, —operating said steam cycle RC with said first working-media-stream EXH1, —expanding at least a part of said first working-media-stream EXH1, namely a third working-media-stream EXH3 by said at least one first steam turbine ST1, —condensing at least a part of said expanded third working-media-stream EXH3, namely a seventh working-media-stream EXH7, by said at least one first water separator CON1, —delivering at least a part of said seventh working-media-stream EXH7 downstream of said first water separator CON1 to a higher pressure level, namely a ninth working-media-stream EXH9, by said at least one first feed-water-pump FWP1, and outputting a feed-water-pump-output-stream by said at least one first feed-water-pump FWP1, —heating at least a part of said feed-water-pump-output-stream, namely a thirteenth working-media-stream EXH13 by at least one first feed-water-preheater WPH1, —feeding at least a part of said thirteenth working-media-stream EXH13 from said steam cycle RC as said first liquid into said recirculation line RCL downstream said at least one first feed water pre-heater WPH1, —extracting a part of working media of said steam cycle RC from said steam cycle RC, particularly downstream said first feed-water-pump FWP1, as a tenth extraction-fluid-stream EXH10, said tenth extraction-fluid-stream EXH10 being particularly water, —extracting a part of said seventh exhaust-fluid-stream EXH7 as carbon-dioxide downstream said first water separator CON1, namely an eighth carbon-dioxide-stream EXH8, —heating said at least one first feed water-preheater WPH1 by an output-stream extracted from said first steam turbine ST1, namely a fifth working-media-stream EXH5.

Just in slightly different wording, the previously explained system and method are substantially equivalent to the following system and method (identical or similar elements are identified by the same reference numerals):

Power generation system comprising—an oxy-fuel-burner (OXB), wherein said oxy-fuel-burner (OXB) is made to generate exhaust-fluid from burning fuel (F) with an oxygen containing gas (O2), which's oxygen content is higher than the oxygen con-tent of ambient air, —a steam cycle (RC) operated with said exhaust-fluid generated by said oxy-fuel-burner (OXB), —a recirculation line (RCL) extracting a part of said exhaust-fluid from said steam cycle (RC) and feeding said exhaust-fluid-stream into said oxy-fuel-burner (OXB) to mix with said continuously generated exhaust-fluid, —wherein said steam cycle (RC) comprises at least one first steam turbine (ST1) expanding at least a part of said exhaust-fluid, namely a third exhaust-fluid-stream (EXH3), —wherein said steam cycle (RC) comprises at least one first condenser (CON1) downstream said first steam turbine (ST1) condensing at least a part of said third exhaust-fluid-stream (EXH3), namely a seventh exhaust-fluid-stream (EXH7), —wherein said steam cycle (RC) comprises at least one first feed-water-pump (FWP1) downstream of said first condenser (CON1) delivering at least a part of said seventh exhaust-fluid-stream (EXH7) to a higher pressure level, namely a ninth exhaust-fluid-stream (EXH9) wherein, said steam cycle (RC) comprises at least one first feed-water-preheater (WPH1) downstream said first feed-water-pump (FWP1) heating at least a part of said seventh exhaust-fluid-stream (EXH7), namely a thirteenth exhaust-fluid-stream (EXH13), —wherein said steam cycle (RC) joins into said recirculation line (RCL) downstream said at least one first feed water pre-heater (WPH1) feeding at least a part of said thirteenth exhaust-fluid-stream (EXH13) into said recirculation line (RCL), namely a nineteenth exhaust-fluid-stream (EXH19), —wherein a part of said ninth exhaust-fluid-stream (EXH9) is extracted from said steam cycle (RC) downstream said first feed-water-pump (FWP1) as a tenth exhaust-fluid-stream (EXH10), —wherein a part of said seventh exhaust-fluid-stream (EXH8) is extracted as carbon-dioxide downstream said first condenser (CON1), namely an eighth exhaust-fluid-stream (EXH8), —wherein said at least one first feed water-preheater (WPH1) is heated with an exhaust-fluid-stream extracted from said first steam turbine (ST1), namely a fifth exhaust-fluid-stream (EXH5).

The corresponding method will be executed on such a system:

Method to operate a power generation system (PGS) defined by the following steps: —generating exhaust-fluid from burning an oxygen containing gas (O2) and fuel (F), —wherein an oxygen content of said oxygen containing gas (O2) is higher than the oxygen content of ambient air, —providing a steam cycle (RC) comprising at least one first steam turbine (ST1), at least one first condenser (CON1) downstream said first steam turbine (ST1), at least one first feed-water-pump (FWP1) downstream said first condenser (CON1), at least one first feed-water-preheater (WPH1) downstream said first feed-water-pump (FWP1), —operating said steam cycle (RC) with said exhaust-fluid generated by said oxy-fuel-burner (OXB), —extracting a part of said exhaust-fluid from said steam cycle (RC) by a recirculation line (RCL) and feeding said exhaust-fluid-stream into said oxy-fuel-burner (OXB) to mix with said continuously generated exhaust-fluid, —expanding at least a part of said exhaust-fluid, namely a third exhaust-fluid-stream (EXH3) by said at least one first steam turbine (ST1), —condensing at least a part of said third exhaust-fluid-stream (EXH3), namely a seventh exhaust-fluid-stream (EXH7), by said at least one first condenser (CON1), —delivering at least a part of said seventh exhaust-fluid-stream (EXH7) downstream of said first condenser (CON1) to a higher pressure level, namely a ninth exhaust-fluid-stream (EXH9), by said at least one first feed-water-pump (FWP1), —heating at least a part of said seventh exhaust-fluid-stream (EXH7), namely a thirteenth exhaust-fluid-stream (EXH13) by at least one first feed-water-preheater (WPH1), —feeding at least a part of said thirteenth exhaust-fluid-stream (EXH13) from said steam cycle (RC) into said recirculation line (RCL), namely a nineteenth exhaust-fluid-stream (EXH19), downstream said at least one first feed water pre-heater (WPH1), —extracting a part of said ninth exhaust-fluid-stream (EXH9) from said steam cycle (RC) downstream said first feed-water-pump (FWP1) as a tenth exhaust-fluid-stream (EXH10), —extracting a part of said seventh exhaust-fluid-stream (EXH8) as carbon-dioxide downstream said first condenser (CON1), namely an eighth exhaust-fluid-stream (EXH8), —heating said at least one first feed water-preheater (WPH1) by an exhaust-fluid-stream extracted from said first steam turbine (ST1), namely a fifth exhaust-fluid-stream (EXH5). 

1. A power generation system (PGS) comprising an oxy-fuel-burner (OXB), wherein said oxy-fuel-burner (OXB) is made to generate a first burner-discharge-fluid from burning fuel (F) with an oxygen containing gas (O2), said oxygen containing gas (O2) having oxygen content which is higher than the oxygen content of ambient air, a recirculation line (RCL) for feeding a first liquid into said oxy-fuel-burner (OXB) to mix with said generated first burner-discharge-fluid to a first working-media-stream (EXH1), a steam cycle (RC) operated with said first working-media-stream (EXH1), wherein said steam cycle (RC) comprises at least one first steam turbine (ST1) expanding at least a part of said first working-media-stream (EXH1), namely a third working-media-stream (EXH3), wherein said first steam turbine (ST1) has at least one output port for expanded fluid, one of which providing a seventh working-media-stream (EXH7), wherein said steam cycle (RC) comprises at least one first water separator (CON1), downstream said first steam turbine (ST1) condensing part of said seventh working-media-stream (EXH7), wherein said first water separator (CON1) has at least one output port for condensed fluid, one of which providing a ninth working-media-stream (EXH9), wherein said steam cycle (RC) comprises at least one first feed-water-pump (FWP1) downstream of said first water separator (CON1) delivering said ninth working-media-stream (EXH9) to a higher pressure level, with an output of a feed-water-pump-output-stream, wherein said steam cycle (RC) comprises at least one first feed-water pre-heater (WPH1) downstream said first feed-water-pump (FWP1) heating at least a part of said feed-water-pump-output-stream, namely a thirteenth working-media-stream (EXH13), wherein said steam cycle (RC) leads into said recirculation line (RCL) downstream said at least one first feed water pre-heater (WPH1) feeding said thirteenth working-media-stream (EXH13) into said recirculation line (RCL) as said first liquid, wherein a part of working media in said steam cycle (RC) is extracted from said steam cycle (RC), as a tenth extraction-fluid-stream (EXH10), said first water separator (CON1) further extracts carbon-dioxide from said seventh working-media-stream (EXH7) via a further output port of said first water separator (CON1) as an eighth carbon-dioxide-stream (EXH8), wherein one of said output ports of said first steam turbine (ST1) provides a fifth working-media-stream (EXH5) and wherein said at least one first feed water-pre-heater (WPH1) is heated via said fifth working-media-stream (EXH5).
 2. The power generation system (PGS) according to claim 1, further comprising a second steam turbine (ST2) downstream of said oxy-fuel-burner (OXB) and upstream of said first steam turbine (ST1) receiving said first working-media-stream (EXH1) from said oxy-fuel-burner (OXB).
 3. The power generation system (PGS) according to claim 2, further comprising a first heat exchanger (HEX1), downstream said oxy-fuel-burner (OXB) and upstream said second steam turbine (ST2) wherein at least a part of said first working-media-stream (EXH1) exiting said second steam turbine (ST2), comprising a third working-media-stream (EXH3) is heated up by said first heat exchanger (HEX1) receiving thermal energy from said first working-media-stream (EXH1).
 4. The power generation system (PGS) according to claim 1, wherein said recirculation line (RCL) comprises at least one adjustable valve (WSV) to control the flow through said recirculation line (RCL).
 5. The power generation system (PGS) according to claim 1, wherein said at least one first feed water-pre-heater (WPH1) comprises a degasification part to collect gaseous working media from the condensing of the provided said fifth working-media-stream (EXH5).
 6. The power generation system (PGS) according to claim 1, further comprising upstream said oxy-fuel-burner (OXB), an air separation unit (ASU) as part of said power generation system (PGS) to provide pure oxygen from ambient air.
 7. A method to operate a power generation system (PGS) comprising: generating a first burner-discharge-fluid from burning an oxygen containing gas (O2) and fuel (F), wherein an oxygen content of said oxygen containing gas (O2) is higher than the oxygen content of ambient air, providing a steam cycle (RC) comprising at least one first steam turbine (ST1), at least one first water separator (CON1), downstream said first steam turbine (ST1), at least one first feed-water-pump (FWP1) downstream said first water separator (CON1), at least one first feed-water-preheater (WPH1) downstream said first feed-water-pump (FWP1), extracting a part of working media from said steam cycle (RC) by a recirculation line (RCL) and feeding a first liquid, as said part of said working media into said oxy-fuel-burner (OXB) to mix with said generated first burner-discharge-fluid to result in a first working-media-stream (EXH1), operating said steam cycle (RC) with said first working-media-stream (EXH1), expanding at least a part of said first working-media-stream (EXH1), comprising a third working-media-stream (EXH3) by said at least one first steam turbine (ST1), outputting a seventh working-media-stream (EXH7) from at least one output port for an expanded fluid of said first steam turbine (ST1), the expanded fluid being a part of said third working-media-stream (EXH3), condensing a part of said seventh working-media-stream (EXH7) by said at least one first water separator (CON1), delivering at least a part of said seventh working-media-stream (EXH7) downstream of said first water separator (CON1) to a higher pressure level, comprising a ninth working-media-stream (EXH9), by said at least one first feed-water-pump (FWP1), and outputting a feed-water-pump-output-stream by said at least one first feed-water-pump (FWP1), heating at least a part of said feed-water-pump-output-stream, comprising a thirteenth working-media-stream (EXH13) by at least one first feed-water-preheater (WPH1), feeding at least a part of said thirteenth working-media-stream (EXH13) from said steam cycle (RC) as said first liquid into said recirculation line (RCL) downstream said at least one first feed water pre-heater (WPH1), extracting a part of working media of said steam cycle (RC) from said steam cycle (RC), as a tenth extraction-fluid-stream (EXH10), extracting a part of said seventh exhaust-fluid-stream (EXH7) as carbon-dioxide downstream said first water separator (CON1), comprising an eighth carbon-dioxide-stream (EXH8), heating said at least one first feed water-preheater (WPH1) by an output-stream extracted from said first steam turbine (ST1), comprising a fifth working-media-stream (EXH5).
 8. The method according to claim 7 further comprising expanding received said first working-media-stream (EXH1) from said oxy-fuel-burner (OXB) by a second steam turbine (ST2) downstream of said oxy-fuel-burner (OXB) and upstream of said first steam turbine (ST1).
 9. The method according to claim 7 further comprising heating up at least a part of said first working-media-stream (EXH1) exiting said second steam turbine (ST2), comprising a third working-media-stream (EXH3) by a first heat exchanger (HEX1) receiving thermal energy from said first working-media-stream (EXH1), said first heat exchanger (HEX1) being provided downstream said oxy-fuel-burner (OXB) and upstream said second steam turbine (ST2).
 10. The method according to claim 7 further comprising controlling the flow through said recirculation line (RCL) by at least one adjustable valve (WSV) or pump or compressor.
 11. The method according to claim 7 further comprising, degasifying to collect gaseous working media from the condensing of the provided said fifth working-media-stream (EXH5).
 12. The method according to claim 7 further comprising, providing an air separation unit (ASU) as part of said power generation system (PGS) to provide pure oxygen from ambient air upstream said oxy-fuel-burner (OXB).
 13. The power generation system (PGS) according to claim 1, wherein the first liquid comprises water.
 14. The power generation system (PGS) according to claim 1, wherein the at least one first water separator (CON1) comprises a condenser.
 15. The power generation system (PGS) according to claim 1, wherein the part of working media in said steam cycle (RC) is extracted from said steam cycle (RC) downstream said first feed-water-pump (FWP1).
 16. The power generation system (PGS) according to claim 1, wherein said tenth extraction-fluid-stream (EXH10) comprises water.
 17. The method according to claim 7, wherein the first liquid comprises water.
 18. The method according to claim 7, wherein the at least one first water separator (CON1) comprises a condenser.
 19. The method according to claim 7, wherein extracting the part of working media of said steam cycle (RC) from said steam cycle (RC) is downstream said first feed-water-pump (FWP1).
 20. The method according to claim 7, wherein said tenth extraction-fluid-stream (EXH10) comprises water. 